Chair or the like with back and seat foldable in upright position

ABSTRACT

A chair of the like used in public halls permitting the occupant when seated to assume an anatomically correct position while permitting both the seat and back to be folded into a substantially vertical position permitting the occupant to rise and stand comfortably while permitting others to pass in front should the chairs be connected together in a row. The chair comprising a support, a seat, first coupling means connecting the support and the seat about a first transverse axis about which the seat rotates, a back, second coupling means connecting the back and seat about a second axis parallel to the first axis permitting the second axis to rotate thereabout, guide means cooperating with the first and second coupling means rotating the back clockwise about the second axis into a generally vertical position as the seat is rotated counterclockwise from a generally horizontal position into a generally vertical position and rotating the back counterclockwise about the second axis into an inclined position as the seat is rotated clockwise into a generally horizontal position and means limiting rotation of the back and seat as aforesaid.

United States Patent Castelli et al.

[1 1 3,656,806 [451 Apr. 18, 1972 [54] CHAIR OR THE LIKE WITH BACK AND SEAT FOLDABLE IN UPRIGHT POSITION [7 2] Inventors: Leonida Castelli; Giancarlo Plretti, both 0 Bologna, Italy [73] Assignee: Anonima Castelli s.a.s., Bologna, Italy [22] Filed: Apr. 13, 1970 [21] App]. No.: 27,524

[30] Foreign Application Priority Data May 23, 1969 Italy ..37,339 A/69 [52] US. Cl ..297/324 [51] Int. Cl ..A47c 1/02 [58] Field of Search ..297/316, 324

[56] References Cited UNITED STATES PATENTS 889,578 6/1908 Brooke ..297/324 2,078,373 4/1937 Dorton ..297/324 FOREIGN PATENTS OR APPLICATIONS 55,208 5/1935 Norway ..297/324 Primary Examiner.'.lames C. Mitchell Attorney-Karl W. Ross [57] ABSTRACT A chair of the like used in public halls permitting the occupant whenseatedto'assume an anatomically correct position while permitting both the seat and back to be folded into a substantially vertical position permitting the occupant to rise and stand comfortably while permitting others to pass in front should the chairs be connected together in a row. The chair comprising a support, a seat, first coupling means connecting the support and the seat about a first transverse axis about which the seat rotates, a back, second coupling means connecting the back and seat about a second axis parallel to the first axis permitting the second axis, to rotate thereabout, guide means cooperating with the first and second coupling means rotating the back clockwise about the second axis into a generally vertical position as the seat is rotated counterclockwise from a generally horizontal position into a generally vertical position and rotating the back counterclockwise about the second axis into an inclined position as the seat is rotated clockwise into a generally horizontal position and means limiting rotation of the back and seat as aforesaid.

8 Claims, 4 Drawing Figures SHEET 3 BF 3 FIG.3

CHAIR OR THE LIKE WITH BACK AND SEAT FOLDABLE IN UPRIGHT POSITION BACKGROUND OF THE INVENTION This invention relates to a chair or the like of the type used in public premises, for example, scholastic or university halls, entertainment places and conference halls, in particular in those places where it is foreseen that the user must remain seated for a considerable time and also have available a reading or writing table. The invention provides a chair which permits the person using it to automatically assume an anatomically correct position, which not only reduces fatigue but prevents the formation of bone malformations such a scolioses should the chair be used as a seat for users of school age. Further, the invention permits both the seat and back to be folded into a substantially vertical position permitting the individual to stand up comfortably in front of said chair and to leave or re-enter his place, if necessary, passing in front of other seats in raised positions when the seats are connected in a row, as in scholastic halls and amphitheatres. It is well known that in the case of chairs or seats in which it is foreseen that the user will sit for a long time it is necessary to arrange and conform the back and the seat in such a manner that they adapt themselves to the correct anatomical position for the occupant. Further, if the seat is associated with a writing and/or reading shelf it is necessary that the shelf have a predetermined, fixed position with respect to the seat because one tends to have the seats and the writing or reading shelf in a fixed position and the user is automatically obliged to arrange himself in the position most anatomically correct. This principle is already known and is of substantial importance, especially in the construction of seats for pupils of school age, since bone malformations and eye defects may result from the use of unsuitable seats. However, the invention relates exclusively to a chair, whether or not it is associated with a reading or writing shelf.

Chairs or the like have already been constructed which answer from an anatomical point of view the foregoing requirements and in which the back is provided with the correct inclination with respect to the plane of the seat for the body of the person seated to be suitable rested. However, where the chair is associated with a desk in front, or is assembled in a row, it is either fixed or at the most has only the seat foldable into the vertical position, where it is necessary to maintain the lines of seats close to each other in order to permit the user to stand up in front of the seat and to leave and reenter the place. Normally, however, access to the seat, even if of the foldable type, is rather uncomfortable, both because the width of passage is constrained by the presence of the desk shelf to the front and because of space economy reasons the rows are close together. Further, the fact that the back must be inclined leads to a chair of considerable bulk, even in the position in which the seat is raised.

Very often the seat is hinged to shelves which project forward, resulting in an obstruction to passage. It thus happens that very often in order to facilitate passage a compromise is reached in which the backs are arranged almost vertically, which from the medical point of view is highly objectionable. Further, the person who sits in such a chair tires rapidly since he is obliged to arrange himself in an irrational position.

OBJECT OF THE INVENTION type.

SUMMARY OF THE INVENTION The present invention provides a chair or the like, which, when occupied, permits the person seated to assume an anatomically correct position, while automatically on raising the seat the plane of the back moves backwards and arranges itself together with the plane of the seat in a vertical position reduced. Further, there are no shelves projecting between the chair and the writing plane or between one chair and another chair in front. Thus, the passageway becomes wider'and not only can one stand up comfortably but also easily pass in front of people who are also standing up in front of their own seats. This is achieved in the present invention by providing'the support for the seat, and that for the back in the form of two pairs of arms connected together and to a pair of base members by two pairs of hinges, the hinges of one pair having their axis of rotation fixed, while the axis of rotation of the other pair of hinges capable of rotating with respect to the fixed axis, to permit the seat and the back to pass from one position to the other, while guide devices compel the parts to carry out foreseen angular excursions, making them automatically pass from the position of minimum bulk to that of utilization and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of the side am'is of the seat and back of the chair in the position of use, showing the area of the hinge of the fixed axis partially in section;

FIG. 2 is a side view showing the chair wherein the seat and back are vertically positioned to minimize the space they ocp) FIG. 3 is an enlarged longitudinal vertical sectional view taken along line A-A of FIG. 4 showing in 'solid line the side arms of the chair in the occupied position and in broken line the arms in vertical storage position; and

FIG. 4 is a transverse sectional view of the side of the chair body taken along line BB of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the drawings, it is seen that the chair which is the object of the invention comprises a support for the back formed of two stanchions 1 (one only shown here) and a support for the seat formed from two arms 2. The members l and 2 of each side are coupled together and slide one into the other. The member 2 is coupled to a base piece 5 and is guided in its movement by guide means provided between the member 1 and the piece 5. A back plane 3 is inserted and fixed between the pair of lateral stanchions 1 and is shaped in a manner suitable for matching the shape of the vertebral column of the occupant in the correct seated position. Between the arms 2 a seat wall 4 is analogously mounted, which is also shaped in such a manner as to embrace and support the posterior parts of the occupant. The walls 3 and 4 are indicated by broken lines and are conventional and not directly related to the invention. It can be seen that as two sides of the chair are independent, they are suitable for the assembly of the back 3 and seat 4 by simple recessing. Screws and other auxiliary fixtures are not necessary. Along the facing sides of the arms 1 and 2 longitudinal grooves la and 2a are formed, respectively, while along the transversal edges of the back 3 and seat 4 flanges 3a and 4a are provided of complementary shape, for inserting into the corresponding grooves la and 2a. First, one of the sides of the chair is assembled. Then, the flanges 3a and 4a are inserted into the corresponding grooves 1a and 2a. Finally, the second side is assembled, the grooves 1a and 2a receiving the facing sides 3a and 4a. It follows that the successive locking of the sides by the system herein disclosedmaintains a perfect connection between the back 3 and stanchion l and between the seat 4 and arms 2 without the need for locking means. It is obvious, however, that the fixing of the back 3 and seat 4 can be carried out by conventional systems. The base members 5 are provided for connecting the pairs of members 1 and 2 to a support device. In the preferred embodiment illustrated, the pieces 5 are inserted by way of a seat 50 formed therein in a cross-piece 6 parallel to the coupling axes, this crosspiece being assembled on legs or fixed supports, which are not shown, and is connected to base members 5 by conventional means. It is obresulting in the bulk of the chair complex being considerably vious that by such a solution, in which at least two chairs are coupled together, a single crossbar 6 can support two or more correctly positioned chairs, the crossbar being supported by at least two stanchions or the like. The seat section 2, 4 is hinged to the pair of base pieces 5, fixed to the crossbar 6 by means of a pair of hinges having their pivots 7 co-axial and in a fixed position, while the back section 1, 3 and the seat section 2, 4 are hinged together by means of a second pair of hinges with co-axial pivots 8, capable of rotating about the axis of the pivots 7.

The supporting structure of one of the identical sides of the chair will now be described. Each arm 2 of the seat, as stated, is pivoted at 7 to the base part and at 8 to the lower extremity of the stanchion 1, the pivot 8 being placed at a certain distance from the pivot 7 so as to permit the group comprising the seat 2, 4 and the back 1, 3 to rotate around the pivot 7. The parts of the members 1, 2 and 5 near the hinges 7 and 8 are shaped in such a. manner as to constitute cam guide systems. For this purpose the upper part of the base member 5a is prolonged forward into two lugs 9 perpendicular with the axes 7 and 8, the lateral external edges of these lugs forming respectively the first section 10a of a cam guide surface, the section which has a convex circular profile, co-axial with the pivot 7 and which is connected to the back with a second edge section 10b, of circular concave shape, whose axis of curvature is situated behind the axis 7 and substantially in the same horizontal plane, the axis of the section 10b coinciding with the limiting position of the pivot 8 in the raised position of the seat and back (FIG. 2). The section 10b is connected to a final section 100 of the cam, a section which is convex and of curvature identical to that of the section 10a. In the internal wall of each lug 9 a recess 9a is formed in the shape of a segment of a circular annulus. The back extremity of each arm 2 about the hinge with the pivot 8 is prolonged in its turn in the form of two lugs 11, perpendicular to the pivot 8, the lateral edges forming a cam surface which comprises starting from the bottom a first concave section 12a, which mates with the section 10a of the cam formed in the body 5, and a second convex section 12b, of curvature complementary to that of the section 10b, the external extremity of the section 12b being connected to the front surface which borders the zone of connection between the stanchions l and the arms 2, in the utilization position of the chair. Lateral hollow zones are formed in each side of the stanchions 1 in a position corresponding to the pivot axis 8. The edges of these zones border each cam and starting from the front wall of each stanchion 1 form a guide surface which comprises a first section 13a mating with the section 12b of the cam surface formed along the edges of the lugs 11 of the arm 2, and successively a second section 13b which rests in the utilization position (FIG. 1) of the chair on the back part of the section 10a formed on the edges of the lugs 9 and on raising of the seat 4 slides over section 106 and finally (FIG. 2) comes to rest on the section 100 of said cam. Between the lugs 9 of the body 5 is inserted a tongue 14 (FIGS. 3 and 4), partially shaped in the form of a disc, which is prolonged behind the arm 2 below the lugs 11. The lower portion of the tongue 14 has an external profile 14a identical with that of the lugs 9, constituting with this and the pivot 7 the cooperating members of the hinge of fixed axis and providing at the same time a guide means between the member 5 and the arm 2. At its front part the hollow area between the two lugs 9 has a circular bottom, so that the part 14a of the tongue 14 can slide on it, this hollow area after a short step 18 being prolonged backwards as a deep longitudinal guide slot 15, whose bottom substantially follows the path of its edges which are shaped like the sections 10b and 10c of the first cam, this slot being provided on its inner side walls with guide grooves 16 parallel to its bottom. From each of the external surfaces of the tongue 14 a wide tooth 20 projects in the form of a circular ring sector, dimensioned so as to be able to slide in the recess or notch 9a during the relative movement of the seat and back, so as to constitute limit stops in combination with the extremities 21a and 21b of said recess or notch, which define the position of utilization of the chair when the member 20 is in contact with the extremity 21a (FIGS. 1 and 3) and the position of minimum bulk wherein there is contact between the member 20 and the stop 21b as shown in FIG. 2.

Between the lugs 11 of the arm 2 is located a tongue projecting wing 17, which projects downwards from'the lower extremity of the stanchion 1, this projecting wing in combination with the lugs 11 forming the hinge body with pivot 8. The projecting wing 17 in turn comprises a circular edge 170 at its lower part which is concentric with the pivot 8 and is designed to slide along a concentric section 140, forming the upper part of the edge of the tongue 14, the edge of which further comprises a back section 141;, slightly inclined forward and hence situated between the section 14a and 140. The projecting wing 17 projects backward in the form of a tail member 27 provided with a front edge 17a which goes with the section 14b of the cam 14 and lies in the guide slot 15 in the open position of the parts (FIGS. 2 and 3), the tail 27 terminating in a roller 19 or other equivalent means mounted on a shaft, the extremities of which are detained and guided by the'grooves 16 of the guide 15. In the closed position (FIG. 2) all the parts of the hinge and guide means penetrate each other and fit together, giving rise to an external side profile of the chair in the form of a continuous line, without projecting parts. In this position each of the pivot 8 is inside the corresponding hinge 7, the position of which is fixed and the planes of the seat'and back are substantially vertical, folded one against the other and moved backwards, so as not to project substantially forward beyond the fixed pivot 7-7, giving the unit the position of minimum bulk and leaving in front of the chair a much wider space than possible with conventional chairs having folded seats. In this position there is contact between the correspond ing sections 13b and 100, 12b and 13a and 10b, and 12a and 10a, while the tail 27 closes the slot 15. This position is further defined by the hold up device, constituted by the corresponding projections 20, which is blocked against the stops 21b. When it is desired to move the parts of the chair to the utilization position, the seat 24 is pulled in the direction of the arrow in FIG. 2. As the anns 2 rotate about their corresponding hinges with the pivot 7, they entrain with themselves, by means of the lugs 11 which act as lever anns and guide means, the second hinges with the pivot 8, and with them the central projecting wings 17 of the stanchions 1, whose tails 27 are detained and guided by means of the rollers 19 and the grooves 16, so that the stanchions l are obliged to carry out an angular movement in synchronism according to a predetermined path, in direction opposite that of lowering of the seat, so as to bring the back 1, 3 to the limit in the inclined position provided and preventing the back from recoiling. During this movement, the sections 120 of the cam edges of the body of the seat descend sliding along the cam section 10a of the pieces 5, the successive section 12b moving away from the section 10b and re-entering its convex seat 13a in the stanchion l by sliding, while the section 13b detaches itself from contact with the cam section until it arrives in the rest position at the end of its travel, on the section 10a (FIG. 1). At the same time the roller 19 rises in the slot 15 until it reaches the step 18, in the almost vertical position of the tail 27, the front edge 17a blocking against the rectilinear section 14b of the cam edge of the tongue 14, while at the same time the projections 20 strike against the corresponding limit stops 21a, the combination of which forms a robust means of arrest between the parts. Consequently the stanchions l and with them the back 3 remain locked in the predetermined utilization position and cannot recede because of the presence of the stops 14b, 17a. The forward movement of the stanchions 1 and with them the back 3 is in turn prevented because of the contact between the stops 21a and the projections 20, thus forming a stop which can be released only by means of rotating the members 2, 4 and 1, 3 around the pivot axis 7, in the direction opposite to the arrow of FIG. 2, gripping the arms 2. From the foregoing specification it can hence be understood that the chair by means of only two pairs of members 1 and 2 and a pair of base pieces 5, in combination with two hinge systems of parallel axes and a suitable cam conformation for guiding the edges of the parts at the junction zone, can be rapidly brought from an inoperative position of minimum bulk to that of utilization, in which the back has an inclined position, rational from the anatomical point of view, while the seat is substantially horizontal. Because of the simplicity of the parts and the means forming the chair of the invention, it is suitable for being produced in a wide range of material and models, and further can be rapidly disassembled and rapidly reassembled which is advantageous from the point of view of storage and transport.

We claim:

1. A chair comprising:

a. a fixed support;

b. a pivotal seat;

c. first coupling means connecting said support and said seat for rotation of said seat about a fixed transverse axis;

. a pivotal back;

. second coupling means on said seat connecting said back and seat for rotation of said back relative to said seat about a displaceable axis parallel to said fixed axis and fixed relative to said seat;

f. guide means adjacent said axes and cooperating with said first and second coupling means for rotating said back in one rotational sense about said displaceable axis into a generally vertical position as said seat is rotated in the other rotational sense from a generally horizontal position into a generally vertical position and for rotating said back in said other sense about said displaceable axis into a generally inclined position as said seat is rotated in said one sense into a generally horizontal position; and

g. stop means adjacent said axes for limiting rotation of said seat and back to the aforesaid positions and including a first stop arrangement on said seat and said support for limiting rotation of said seat relative to said support and a second stop arrangement for limiting rotation of said back relative to said seat and said support.

2. A chair comprising;

a fixed support including a pair of base pieces;

a pivotal seat including a pair of lateral seat arms shaped to receive between them a seat wall;

first coupling means including a first hinge connecting said support and said seat for rotation of said seat about a fixed transverse axis;

a pivotal back including a pair of lateral stanchions shaped to receive them a back wall;

second coupling means on said seat including a second hinge connecting said back and said seat for rotation of said back relative to said seat about a dispaceable axis parallel to said fixed axis and fixed relative to said seat, one such base piece, one such stanchion, one such seat arm one such first hinge, and one such second hinge constituting a side of said seat;

guide means to each side of said seat cooperating with said first and second coupling means for rotating said back in one rotational sense about said displaceable axis into a generally vertical position as said seat is rotated in the other rotational sense from a generally horizontal position into a generally vertical position and for rotating said back in said other sense about said displaceable axis into a generally inclined position as said seat is rotated in said one sense into a generally horizontal position; and

stop means to each side of said seat and adjacent said axes for limiting rotation of said seat and back to the aforesaid positions and including a first stop arrangement on said seat and said support for limiting rotation of said seat relative to said support and a second stop arrangement for limiting rotation of said back relative to said seat.

3. A chair as defined in claim 2, in which the seat comprises two lateral seat arms sloped to receive a seat wall between them, the back being formed from two lateral stanchions shaped to receive between them a back wall the support being formed from two separate base pieces, each side of the chair compnses one such seat arm, one such back stanchion, one such base piece, and first and second hinges interconnection them, the first hinge forming part of the first coupling means and the second hinge forming part of the second coupling means guide and stop means being provided at each of said sides.

4. A chair as defined in claim 2, in which the first hinge comprises hinge members in the form of respective lugs formed on the base pieces and a wing projecting from the back extremity of each seat arm, said hinge members having edges which constitute part of a first section of a first cam and countercam guide system having a cam formed by the edge of the base piece and a counter cam formed by the back extremity of the seat arm, a second cam guide system being provided between said countercam and an edge shaped as a cam formed at the lower extremity of the stanchion on'at least one side thereof, this latter cam having its back part shaped in such a manner as to co-operate with the first cam only at the beginning and at the end of the movement accomplished by the parts for passing from one position to the other while in the intermediate phase it remains separated from it.

5. A chair as defined in claim 2 in which the back part of each arm of the seat is shaped in such a manner as to form two lugs perpendicular to the coupling axes and constituting, in combination with a wing projecting downwardly from the corresponding stanchion, the members of the hinge which form part of the second hinge between the seat and back, the edges of said lugs on said arms in combination with the edges of the base piece and the lower extremity of the stanchion being shaped as guide cam members, adapted to match one another in such a manner as to form a substantially continuous surface in many mutual positions assumed by the parts.

6. A chair as defined in claim 5, in which between the hinge members in the form of lugs which project form the base piece a recess if formed in which the wing is located which is part of the seat arm, each arm being formed with a tail carrying a sliding roller on a shaft, said recess being extended backwards after a small step as a longitudinal guide slot whose bottom has a form substantially parallel to the form of the back part of the first cam, guide grooves being formed in the internal side walls of said slot parallel to the bottom and housing the extremities of the shaft of said sliding roller fixed to said tail which has a form complementary to said slot and which fills it in the closed position of the complex, said tail being prolonged backwards by a projecting part which fonns a member of the second hinge and which constitutes the guide means for making the back carry out its relative rotary movements with respect to the seat, so as to pass from the operative position to the inoperative position and vice versa.

7. A chair as defined in claim 6, in which the tail has a front part of planar outline which in the operative position of the seat is disposed in a substantially vertical position and is housed above an identically outlined section of the wing projecting from the arm of the seat, and constituting in this manner the second stop arrangement which prevents the back from moving back with respect to the seat in the operative position of the chair, this second stop arrangement becoming inoperative only as a consequence of a rotation of the tail caused by raising the seat which causes the second hinge to rotate with respect to the first.

8. A chair as defined in claim 7, in which two stop arrangements are formed between the lugs of the base piece and the wing forming a body with the arm of the seat, a recess in the form of a segment of a circular annulus being formed in one of the two oversides facing said hinge elements and the other having a projection which slides inside said recess during the relative rotation of said hinge members, each recess cooperating with its projection being so shaped as to engage against one in the position of use of the chair and with the other extremity thereof in the position of minimum bulk of the chair. 

1. A chair comprising: a. a fixed support; b. a pivotal seat; c. first coupling means connecting said support and said seat for rotation of said seat about a fixed transverse axis; d. a pivotal back; e. second coupling means on said seat connecting said back and seat for rotation of said back relative tO said seat about a displaceable axis parallel to said fixed axis and fixed relative to said seat; f. guide means adjacent said axes and cooperating with said first and second coupling means for rotating said back in one rotational sense about said displaceable axis into a generally vertical position as said seat is rotated in the other rotational sense from a generally horizontal position into a generally vertical position and for rotating said back in said other sense about said displaceable axis into a generally inclined position as said seat is rotated in said one sense into a generally horizontal position; and g. stop means adjacent said axes for limiting rotation of said seat and back to the aforesaid positions and including a first stop arrangement on said seat and said support for limiting rotation of said seat relative to said support and a second stop arrangement for limiting rotation of said back relative to said seat and said support.
 2. A chair comprising; a fixed support including a pair of base pieces; a pivotal seat including a pair of lateral seat arms shaped to receive between them a seat wall; first coupling means including a first hinge connecting said support and said seat for rotation of said seat about a fixed transverse axis; a pivotal back including a pair of lateral stanchions shaped to receive them a back wall; second coupling means on said seat including a second hinge connecting said back and said seat for rotation of said back relative to said seat about a dispaceable axis parallel to said fixed axis and fixed relative to said seat, one such base piece, one such stanchion, one such seat arm one such first hinge, and one such second hinge constituting a side of said seat; guide means to each side of said seat cooperating with said first and second coupling means for rotating said back in one rotational sense about said displaceable axis into a generally vertical position as said seat is rotated in the other rotational sense from a generally horizontal position into a generally vertical position and for rotating said back in said other sense about said displaceable axis into a generally inclined position as said seat is rotated in said one sense into a generally horizontal position; and stop means to each side of said seat and adjacent said axes for limiting rotation of said seat and back to the aforesaid positions and including a first stop arrangement on said seat and said support for limiting rotation of said seat relative to said support and a second stop arrangement for limiting rotation of said back relative to said seat.
 3. A chair as defined in claim 2, in which the seat comprises two lateral seat arms sloped to receive a seat wall between them, the back being formed from two lateral stanchions shaped to receive between them a back wall the support being formed from two separate base pieces, each side of the chair comprises one such seat arm, one such back stanchion, one such base piece, and first and second hinges interconnection them, the first hinge forming part of the first coupling means and the second hinge forming part of the second coupling means guide and stop means being provided at each of said sides.
 4. A chair as defined in claim 2, in which the first hinge comprises hinge members in the form of respective lugs formed on the base pieces and a wing projecting from the back extremity of each seat arm, said hinge members having edges which constitute part of a first section of a first cam and countercam guide system having a cam formed by the edge of the base piece and a counter cam formed by the back extremity of the seat arm, a second cam guide system being provided between said countercam and an edge shaped as a cam formed at the lower extremity of the stanchion on at least one side thereof, this latter cam having its back part shaped in such a manner as to co-operate with the first cam only at the beginning and at the end of the movement accomplished by the parts for passiNg from one position to the other while in the intermediate phase it remains separated from it.
 5. A chair as defined in claim 2 in which the back part of each arm of the seat is shaped in such a manner as to form two lugs perpendicular to the coupling axes and constituting, in combination with a wing projecting downwardly from the corresponding stanchion, the members of the hinge which form part of the second hinge between the seat and back, the edges of said lugs on said arms in combination with the edges of the base piece and the lower extremity of the stanchion being shaped as guide cam members, adapted to match one another in such a manner as to form a substantially continuous surface in many mutual positions assumed by the parts.
 6. A chair as defined in claim 5, in which between the hinge members in the form of lugs which project form the base piece a recess if formed in which the wing is located which is part of the seat arm, each arm being formed with a tail carrying a sliding roller on a shaft, said recess being extended backwards after a small step as a longitudinal guide slot whose bottom has a form substantially parallel to the form of the back part of the first cam, guide grooves being formed in the internal side walls of said slot parallel to the bottom and housing the extremities of the shaft of said sliding roller fixed to said tail which has a form complementary to said slot and which fills it in the closed position of the complex, said tail being prolonged backwards by a projecting part which forms a member of the second hinge and which constitutes the guide means for making the back carry out its relative rotary movements with respect to the seat, so as to pass from the operative position to the inoperative position and vice versa.
 7. A chair as defined in claim 6, in which the tail has a front part of planar outline which in the operative position of the seat is disposed in a substantially vertical position and is housed above an identically outlined section of the wing projecting from the arm of the seat, and constituting in this manner the second stop arrangement which prevents the back from moving back with respect to the seat in the operative position of the chair, this second stop arrangement becoming inoperative only as a consequence of a rotation of the tail caused by raising the seat which causes the second hinge to rotate with respect to the first.
 8. A chair as defined in claim 7, in which two stop arrangements are formed between the lugs of the base piece and the wing forming a body with the arm of the seat, a recess in the form of a segment of a circular annulus being formed in one of the two oversides facing said hinge elements and the other having a projection which slides inside said recess during the relative rotation of said hinge members, each recess co-operating with its projection being so shaped as to engage against one in the position of use of the chair and with the other extremity thereof in the position of minimum bulk of the chair. 